Before Charles Darwin: Influential Theories of Evolution from the 18th Century

The eighteenth-century European Enlightenment was a tumultuous time of great change and new ideas. Later, in the nineteenth-century, Charles Darwin would come out with his theory of evolution, which stated that species evolved slowly over time through the process of natural selection. The process of natural selection is better known as “the process that produces adaptation”.[1]

Darwin’s ideas, in a world which still strongly believed that the Earth had been created by God in seven days, were highly controversial, since his findings suggested that humans were animals. Yet, Darwin was not the first to question how life changes over time. In the century preceding Darwin, several scientists were working on theories of their own which were equally controversial. In many ways, Charles Darwin is indebted to the scientists of the eighteenth century whose work he expanded on to come up with his own theories.

One of the first scientists to question the origins of Man in the eighteenth century was George Louis Leclerc, Comte de Buffon. In his book Natural History, General and Particular, he described in detail the known natural world including common traits he observed and the differences between animals of the same species.[2] Part of what Leclerc was observing was variation within groups, better understood as “differences in phenotype or genotype between individuals in a particular group”.[3] However, because Leclerc was only observing variations in phenotype.

Along with his observations on variation among species, Leclerc dedicated an entire section on the “Nomenclature of Apes.” Leclerc defined an ape in this section of his book as “an animal without a tail, whose face is flat, whose teeth, hands, fingers, and nails resemble those of man, and who, like him, walks erect on two feet”.[4] In his writings on the “Nomenclature of Apes,” Leclerc observed how certain species of apes had similar physical traits and appearances to humans. He acknowledged in this volume “that the ape might be a variety of the human species” and that perhaps “the Creator did not form man’s body on a model absolutely different from that of a mere animal’s”.[5] This, though still leaning towards creationist ideas begins to hint at humans and apes being somehow linked together.

Leclerc, though wrong about apes being a form of human species, seemed to realize that men and apes had too much in common to not be related somehow. Today, through further testing it is now known that humans and primates are linked genetically. At the time however, Leclerc lacked what was necessary to prove this knowledge and therefore could only speculate from what he was observing.

Furthermore, his statement about how the Creator formed man’s body hints at the same idea that became so controversial with Charles Darwin; that man is just another animal. These ideas for Leclerc’s time were, in themselves highly controversial because they challenged the church’s beliefs. However, following right behind Leclerc was Erasmus Darwin, whose ideas were also highly controversial and disputed.

Today, Erasmus Darwin earns most of the credit in the scientific community for recognizing and describing biological evolution.[6] Darwin observed that certain traits were passed down from parents to offspring. He particularly noted that by breeding certain types of a species together one could achieve desired traits in the offspring. He noted that an example could be made from horses and how they were bred “for the different purposes of strength or swiftness, in carrying burdens or running races”.[7]

Darwin’s observations are in part touching on Gregor Mendel’s theory of heredity.[8] He was observing the passing down of genes to offspring from their parents through “breeding inheritance“.[9] In this case he was observing the process through what is now known as artificial selection. Here humans take control on what traits are passed down to the offspring by selecting parents with particular desired traits.[10] However, Darwin also noted that the passing down of certain traits occurred naturally as well. Darwin noted that certain mutations in animals kept appearing down through the generations and used the example of “a breed of cats with an additional claw on each foot”.[11]

Darwin also observed that these changes took time to occur. This led him to be uncertain about how old the Earth was by the church’s standards. Instead he accurately stated that the Earth was most likely much older and estimated the time scale of evolution to take “millions of ages”.[12] Furthermore, Darwin also had very insightful ideas about how life formed on Earth. His theory of evolution is most accurately depicted in his poem The Temple of Nature. In the poem, Darwin speculates that life began in the ocean as “tiny specs” by spontaneous generation. He goes on to say that after a time the “specs” evolved and changed; and then animals were “born” from the sea.[13] While highly accurate, Darwin’s one big problem was his belief that life sprang from spontaneous generation or the idea that life could suddenly spring from nothing. However, as extensive as his observations were, Darwin was never able to prove his ideas to the rest of the world due to lack of evidence at the time.[14]

Following with a similar theory of evolution to Erasmus Darwin’s was Jean-Baptiste Lamarck. However, Lamarck and Darwin differed slightly on how organic evolution took place. Lamarck believed that organic evolution occurred through “modifications which arise from the greater or lesser use of any part, due to some environmental cause”.[15] Lamarck argued in his book Zoological Philosophy that because of this, species did not have an absolute constancy in nature. He believed that every species had “derived from the action of the environment in which it has long been placed the habits which we find in it”.[16]

Lamarck pointed out that a species only stayed in a “constant state” as long as the conditions in which it had originally adapted to remained constant. When an individual of a particular species changed their living conditions due to “climate, habits, or manner of life” Lamarck believed that these individuals then were subjected to influences which imposed change.[17] This in turn would slightly alter the species in some way or form through the process of mutation.[18] Further, he stated that variation of a species occurred due to slight variations on the conditions of that particular species’ environment.[19]

Lamarck, like Erasmus Darwin, observed that changes in species occurred slowly over time. He inferred that change occurred so slowly over time that it would be impossible to observe. Therefore, one could only prove this by “an inspection of ancient monuments”.[20] Furthermore, Lamarck went on to propose that because things have undergone change in the past that one could infer that they would continue to change in the future.[21]

By studying various species, Lamarck noted that species who had undergone some kind change but were only a few generations apart varied only slightly. However, he observed that when comparing the same species over many generations the variations were greater and more distinguishable. He then proposed that with time, favorable conditions, and new habits to modify the species then led to the current forms of the species of his time.[22]

Lamarck also argued that the adaptation of a particular species over time would affect and eventually alter the environment that particular species inhabited as well. He stated that if a new environment “induces new habits in animals” then the animals would have different needs.[23] This in turn would then force the environment to change in order to accommodate the new needs of the animals in order to sustain them.[24]

Lamarck’s ideas strongly opposed the church’s views. At the time, the church believed that everything had remained the same since Creation. Lamarck attempted to correct this by stating that “nothing exists but by the will of a Sublime Creator of all things”.[25] However, he questioned whether or not rules could be put into place for the “execution of the Creator’s will”.[26]

However, while Lamarck provided plenty of observations about life changing over time, he failed to incorporate extinction into his theory. His theory of life changing and adapting due to environmental changes was highly disputed by Georges Cuvier. Cuvier eventually disproved Lamarck’s theory by establishing that extinction was real from studying fossils of life forms that no longer existed.

Cuvier first noted that “bones of enormous animals” were found in various locations around the world such as Northern Europe, Asia, and America.[27] He observed that the bones, while resembling animals that were in existence, were found in places that could not belong to any species living in that area at the time. Some of the bones found in Northern Europe resembled those of elephants closely in form and others resembled those of a rhinoceros. Yet, elephants and rhinoceros only existed in “the tropical zone of the Old World”.[28] However, upon further examination of the bones, Cuvier concluded that while the creatures were similar to elephants and rhinoceros they could not be absolutely the same species.

These fossil remains lead Cuvier to believe in the “existence of a previous world to ours” that was “destroyed by some kind of catastrophe”.[29] Later findings of fossils buried at different depths, along with the types of species that were uncovered such as underwater animals, would allow him to theorize that there were in fact several previous worlds before ours. From these findings, Cuvier was also able to make geological observations which helped support his theory and to shape the idea that Earth had had a violent past.

Cuvier noted that in flat planes, when one penetrated the Earth deep enough, there was evidence of organic life forms strictly belonging to the ocean. Comparable beds or layers containing similar fossils could be seen when excavating the side of a hill as well. This provided evidence that at some point in the past, parts of dry land had been covered by ocean.[30] With this information Cuvier was then able to prove that the Earth had gone through several transformations over time. He explained how “the more ancient the beds, the more each of them was uniform over a wide expanse” whereas “the newer the beds, the more limited and the more subjected they were to variation over small distances”.[31] Therefore, because of this the “catastrophes that produced revolutions” slightly altered how silt, rock, and organic matter were deposited over time forming layers that could then be observed.[32]

The final and perhaps most famously influential scientist to Charles Darwin was geologist Charles Lyell. Lyell stated that with the advances in science, particularly in geology and evolutionary theory, religion, in many ways was rendered obsolete. He believed that “the moral and physical world are explained, and instead of being due to extrinsic and irregular causes they are found to depend on fixed and invariable laws.”[33]

Like Cuvier, Lyell observed that when one placed “fossiliferous formations in chronological order, they constituted a broken and defective series of monuments” which showed evidence of past epochs.[34] Also like Cuvier, he believed that the planet switched between states of tranquility and convulsion. This in turn allowed for “great and sudden revolutions in the geological order of events”.[35]

Lyell agreed, due to his observations and studies, that life changes slowly over time. This idea not only applies to living species, but also “simultaneously applies everywhere throughout the habitable surface of sea and land”.[36]

Lyell’s observations of the various strata lead him to come up with a very similar theory of evolution to that of Cuvier’s as well. He believed that not only could one determine change over the passage of time from the layers of strata, but from the remains of organic matter left behind inside the strata. He concluded “that at successive periods distinct tribes of animals and plants have inhabited the land and waters”.[37] Furthermore, he observed that the animal remains trapped in the newer strata were more similar to the animals of the time. This lead Lyell to describe life as being a “state of continual flux” and that “there were many reasons for the extinction of a particular species”.[38] The reason for this being that they were unfit to survive in their environment. However, Lyell noted that some living species do resembled at least in part their extinct counterparts.

Throughout the eighteenth century various scientific theories about the Earth’s geology and human evolution arose. Beginning at the turn of the century, George Louis Leclerc, Comte de Buffon observed variation among different species and similarities between man and apes. Following Leclerc was Charles Darwin’s grandfather Erasmus Darwin. Today he is known best for describing biological evolution. Along with that Erasmus Darwin was one of the first to very accurately claim that the Earth was much older than the church claimed, though he was never able to prove any of his findings.

With similar ideas to Erasmus Darwin, Lamarck then claimed that species could change over time due to changes in their environment. However, what Lamarck failed to include in his theory was the possibility of extinction. Georges Cuvier quickly came along and corrected this error, disproving Lamarck’s theory of evolution in the process. His studies on fossils and geology were the basis on what Charles Lyell later expanded on. These theories and the scientists who created them, though not always accurate, helped pave the way for Charles Darwin and his Theory of Evolution.